How to export multiple NLAtracks to a single .fbx file in blender 2.80?
I'm not sure what your use case is, but I'm using this to import animations into Unity game engine. The NLA tracks thing doesn't seem to work with 2.8 and Unity, but you can have several actions created in the Dope Sheet --> Action Editor, and when you export, select "All Actions":



One thing that messed me up was that you have to completely delete the .fbx file and create a new one in order for Unity to recognize it properly and update the list of animations. Reimporting or refreshing doesn't work if you just replace the file that was already there.